The present invention relates generally to the data processing field, and more particularly, relates to a method and apparatus for optimizing corner frequency calibration of a tunable filter over a wide range of frequencies in a data channel of a direct access storage device (DASD).
Direct access storage devices (DASDs) often incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks. Typically servo information is provided on one or more disk surfaces for reading by the transducer heads for accurately and reliably positioning transducer heads on the disk surfaces at a specific location to read and write data.
In complementary metal oxide semiconductor (CMOS) technologies the process variations can be made very easily to tune the process to be faster or slower as the need may be. This kind of predictable as well as controlled variation affects analog circuits the most. In the DASD data channel, a tunable filter, such as a low pass continuous time filter (CTF) used for filtering readback signals, is especially sensitive to such changes. This filter must operate over a wide range of frequencies from a low frequency servo readback signal to a high frequency data readback signal. For example, the servo readback signal can be a 40 MHz signal and the data readback signal can be a 325 MHz signal.
As channel speeds go faster, conventional arrangements of circuit functions can be a limiting factor in overall performance. In the design of new DASDs, the performance requirements can be more demanding than the data channel can deliver with traditional architectures.
A need exist for an improved mechanism for optimizing calibration of a corner frequency of a tunable filter over a wide range of frequencies in a data channel of a direct access storage device (DASD). Corner frequency calibration (CFC) takes the place of fuse trims in older technologies. Corner frequency calibration leads to tremendous test and technology savings over fuse trims.
A principal object of the present invention is to provide a method and apparatus for optimizing calibration of a corner frequency of a tunable filter over a wide range of frequencies in a data channel of a direct access storage device (DASD). Other important objects of the present invention are to provide such methods and apparatus for optimizing corner frequency calibration substantially without negative effect and that overcome many of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for optimizing calibration of a tunable filter over a wide range of frequencies in a data channel of a direct access storage device (DASD). Calibration codes are received for low corner frequency, banding, and high corner frequency. A programmable diode is provided with a DC portion and a tunable digital-to-analog converter (DAC). A calibration control current is generated for calibrating the tunable filter utilizing the programmable diode and the calibration codes.
In accordance with features of the invention, the programmable diode is used to vary the calibration control current to calibrate the tunable filter to a correct low corner frequency and high corner frequency. The programmable diode can be programmed over a large range.